The present invention relates to ground fault circuit interrupting (GFCI) devices and particularly to an improved GFCI module therefor.
GFCI devices are presently enjoying wide application in certain residential circuits, on construction sites and in industry to protect personnel from potentially injurious electrical shock should they become involved in a line-to-ground fault. These devices are available in either a circuit breaker configuration acceptable in a conventional circuit breaker load center or a receptacle configuration acceptable in a conventional wall outlet box. To achieve their acceptability in such existing facilities, GFCI devices must be dimensionally comparable to conventional circuit breakers and outlet receptacles lacking ground fault protection capability. Consequently, the components operating to afford ground fault protection must be highly miniaturized to accommodate being packaged in very little available space.
As is well understood in the art, the circuit interruption function is precipitated by current activation of a trip solenoid whose operating coil is connected in series with a thyristor between the line and neutral sides of the circuit in which the GFCI device is installed. Since the typical thyristor utilized is a silicon controlled rectifier (SCR), a uni-directional current conducting device, when a circuit interruption or trip function is called for, the SCR should be triggered into induction early in those half-cycles of the AC line voltage for which the SCR is forwardly biased. Under these circumstances, the SCR should conduct adequate current for a sufficient period of time to achieve the requisite mechanical trip initiating response of the trip solenoid. However, especially when the ground fault signal developed in the differential current transformer secondary winding in response to a ground fault indicative imbalance in the currents flowing in the line and neutral conductors is just slightly in excess of the established trip threshold level, problems have occasionally been encountered in achieving reliable tripping actuation of the trip solenoid. This is due to the failure to deliver a sufficient hard gate triggering pulse to the SCR or the triggering pulse occurs too late in the SCR conductive half-cycle.
It is accordingly an object of the present invention to provide an improved ground fault circuit interrupting device.
A further object is to provide a ground fault circuit interrupting device of the above character wherein initiation of a circuit interrupting function is achieved in a more reliable fashion.
An additional object is to provide a ground fault circuit interrupting device of the above character which is inexpensive to manufacture and efficient in construction.
Other objects of the invention will in part be obvious and in part appear hereinafter.